【作者】 王佳；

【导师】 宁兴坤； 王淑芳；

【作者基本信息】 河北大学 ， 凝聚态物理， 2022， 硕士

【摘要】 硒化铅（PbSe）由于具有可调谐的带隙（0.28-1.2 e V）和较大的载流子迁移率,是一种优异的半导体热电材料。近年来,通过各种手段的调控,PbSe材料的热电性能得到了迅速发展,成为中温段（500-900 K）内高效的热电材料之一,可与碲化铅（Pb Te）材料相媲美。与块体材料相比,薄膜与现代半导体技术具有更强的兼容性,在热电器件的构造和应用方面具有独特的优势。然而PbSe在低温范围（300-523 K）内较低的热电性能阻碍了其实际应用,需要加以克服。本文采用脉冲激光沉积（PLD）技术,通过引入第二相纳米结构对PbSe薄膜的低温热电性能进行了调控研究。主要研究内容及结论如下:（1）垂直界面对PbSe薄膜热电性能的调控研究:利用PLD技术在Sr Ti O₃（001）衬底上制备了具有自组装垂直纳米柱排列结构的n型PbSe:Au纳米复合薄膜,对其微观结构和热电性能进行了详细的研究。研究发现垂直纳米微结构可以用来提高PbSe的热电性能:一方面,PbSe:Au复合薄膜中存在的垂直界面有利于增强能量过滤效应,增大Seebeck系数;另一方面,PbSe/Au垂直界面存在高密度位错,大幅降低了面内热导率。高的Seebeck系数和低的热导率使得PbSe:Au复合薄膜的ZT值在523 K时达到了2.6,其室温ZT值由0.05提高至0.2。（2）Pb自补偿对PbSe薄膜热电性能的调控研究:利用PLD技术在Sr Ti O₃（001）衬底上制备了PbSe:Pb纳米复合薄膜,对其微观结构和热电性能进行了详细的研究。研究结果表明第二相Pb的含量可以有效地调控其热电性能。一方面,少量的Pb掺杂使得PbSe:Pb薄膜由p型转变为n型;另一方面,随着Pb含量的继续增大,第二相Pb逐渐析出,形成PbSe:Pb纳米复合薄膜,其在300-523 K温度区间内具有优异的导电性能,PF_avg从5.69μW cm^-1 K^-2提升到20μW cm^-1 K^-2,室温ZT值达到0.43。（3）逾渗理论对PbSe薄膜热电性能的调控研究:利用PLD技术在Sr Ti O₃（001）衬底上制备了不同Ag含量的PbSe:Ag纳米复合薄膜,对其微观结构和热电性能进行了详细的研究。研究发现,当PbSe:Ag体积比为75:25时,复合薄膜达到了其导电的逾渗阈值,载流子浓度从2.36×10¹⁹ cm^-3提高到7.45×10¹⁹ cm^-3。此外,PbSe:Ag边界形成了Ag₂Se相,PbSe:Ag₂Se:Ag晶界和位错可以有效地降低热导率。在300-523 K温度范围内,（PbSe）₇₅:（Ag）₂₅样品的PF_avg～37.83μW cm^-1 K^-2,室温ZT值达到0.63。更多还原

【Abstract】 Lead selenide（PbSe）is one of the promising thermoelectric semiconductor materials due to its tunable band gap（0.28-1.2 e V）and large carrier mobility.In recent years,the thermoelectric properties of PbSe have been rapidly developed by various means to become one of the most efficient n-type thermoelectric materials in the mid-temperature range（500-900 K）,comparable to lead telluride（Pb Te）.Compared to bulk materials,thin films have greater compatibility with modern semiconductor technology and offer unique advantages in the construction and application of thermoelectric devices.However,the low thermoelectric properties of PbSe in the low temperature range（300-523 K）hinder its practical application and need to be overcome.In this paper,the thermoelectric properties of PbSe thin films at low-temperature were investigated by pulsed laser deposition（PLD）technology through introducing second-phase nanostructures.The main research contents and conclusions are as follows.（1）Effect of vertical interface on thermoelectric properties of PbSe thin films:PbSe:Au thin films with self-assembled vertically nanopillars structure were prepared on Sr Ti O₃（001）substrate by PLD technology.The microstructure and thermoelectric properties of PbSe:Au thin films were studied in detail.It was found that vertical nanomicrostructures could improve the thermoelectric properties of PbSe:on the one hand,the vertical interfaces in PbSe:Au composite films is beneficial to enhance the energy filtering effect and enhance the Seebeck coefficient of thin films;on the other hand,the high density dislocations at the PbSe/Au vertical interface drastically reduced the in-plane thermal conductivity.The ZT value of the PbSe:Au composite film reached 2.6 at 523 K because of the high Seebeck coefficient and low thermal conductivity,and the ZT value from 0.02 to 0.2 at room temperature.（2）Effect of Pb self-compensation on the thermoelectric properties of PbSe thin films:We have prepared PbSe:Pb nanocomposite films on Sr Ti O₃（001）substrates by PLD technology and investigated their microstructure and thermoelectric properties in detail.The results show that the content of the second phase Pb can effectively modulate its thermoelectric properties.On the one hand,a small amount of Pb doping transforms the transport of PbSe:Pb thin film from p-type to n-type;on the other hand,with the increase of Pb content,the second-phase Pb was gradually precipitated and formed PbSe:Pb nanocomposite films.The PF_avg was enhanced from 5.69μW cm^-1 K^-2 to 20μW cm^-1 K^-2 in the temperature range of 300-523 K,which have excellent electrical properties.The ZT value of the nanocompsite film can reached 0.43 at room temperature.（3）Effect of percolation theory on the thermoelectric properties of PbSe thin film:We prepared PbSe:Ag films with different Ag contents on Sr Ti O₃（001）substrates by PLD technology and studied their microstructure and thermoelectric properties in detail.When the ratio of PbSe:Ag is 75:25,Ag reached the percolation threshold and the carrier concentration increased from 2.36×10¹⁹ cm^-3 to 7.45×10¹⁹ cm^-3.In addition,the Ag₂Se phase is formed at the PbSe:Ag boundary.The grain boundaries and dislocations of PbSe:Ag₂Se:Ag can effectively reduce the thermal conductivity.The PF_avg of the（PbSe）₇₅:（Ag）₂₅ sample was～37.83μW cm^-1 K^-2 in the temperature range of 300-523 K,and the ZT value reached 0.63 at room temperature.更多还原